How to figure prop size? help,Hank LM maybe?

[big easy]

I need to get a prop for my project boat,and have a question for anyone with knowledge on the subject.

I picked up a nice used Mercruiser Alpha drive with a 350 250hp engine.It runs perfect,and it was in a 19' Chris Craft Scorpion.This engine has less than 400 hrs,and was a new replacement just two years ago.The drive is also in perfect shape.l

I installed this package in my 23' Seacraft.The total weight for the boat,people,engines,fuel,tackle and every single thing i can think of is in the vicinity of 5500to 5800 lbs.

All the prop calculators online show a a prop size of approx 15" diameter X 16 pitch.

I'm a little confused as the prop that was on the drive was a 14" X 26 pitch.I'm assuming it's because it was on a smaller lighter boat.I was worried about the gear ratio on the outdrive,as all the serial #'s are worn off,but all the mechanics i spoke to told me that if it was a drive on a V8 350,then it's almost positive that the ratio is 1:50 to 1.(late eighties).

So many of the sizing charts don't consider the boat weight

Can anyone tell me if the pitch would be so different between boats because of boat weight,or is it gear ratio.Any info would be a huge help to me.

[goingagain2]

big easy

I run a 2359 trophy,prob about same weight or close, 350 with alfa one

gen2 and i think 150-1 ratio. use (or try) 14 1/2 X 17 pitch prob, think that will do it for you. good luck with it.

john

[L&M]

John R: I know the boat your powering well and your weight estimate is real close.

IF That drive is the original for that engine it is a 1:50 ratio and a 15x16 or 15 1/4X15c should put you in the ball park. But unless it was a very light boat a 26 pitch prop would indicate that it might not be the ratio you think it is. There's only one way to know for certain what you have and that' to pull the top cover (4- 3/8's 12 point bolts) and count the teeth on gears. You'll want to know what your working with before ya start spending $$ on props. Any problems or questions pm your # and I'll give a call.

[big easy]

Wow!thanks for the quick replies guys.Thanks for the offer Hank,I'll pull the cover tonight and count the teeth on the gears.Anything else i should know about the gears?can I count them all from the top view,or do i have to turn over the engine to count the teeth?I'll pm you after I make the attempt.

Thanks again.